One Reddit user said that the park next to their house has a Bulbasaur nest that will only be activated when the Pokemon Go app will go into night mode. So it means that it seems like a nocturnal nest. One user also said that the Kabuto nest that he noticed rarely spawns during the day, but when night time comes, it spawns more frequently than during the day.
A Charmander nest was also noticed to have a slow spawning rate during 2:00 PM to 5:00 PM. Only a few or no Charmander can be seen during these hours. So I means that players may be interested to hunt more Pokemon at night, in the hope that better nests could be seen. The nests have been slowly changing, and its recent update also brought with it the Spawning evolution of base Pokemon. One example are Charmander Nests that now spawns Charizard and Chameleon.
SpiralHamHOUSTON of Reddit also claimed that he experience a similar thing around 3:00 AM. He found out that a non-nest had transformed into a Kabuto nest, and he saw five Kabuto at once. He checked during the day, and he found only one in every 30 minutes.
It was also noticed that prior to the latest migration, all nests have a pattern. This pattern can be described as - nests stop spawning at night if the park closed at night; but the nests that were located in open parks will spawn 24/7. This was posted by Reddit user xillaxv.